They often seem to form overnight and once in the water are difficult to get rid of. Algae colonize the pool when the water parameters are no longer within the normal range. Precautions are important to keep the pool water clean.

Algae in the pool can have various causes

Table of Contents

Show all
  1. the essentials in brief
  2. Types of algae in the pool
  3. cause of algae growth
  4. Remove and fight
  5. Inappropriate means
  6. home remedies
  7. water treatment
  8. frequently asked Questions

    9. the essentials in brief

    • Algae develop when the pH value is too high, when there is a high nutrient content and heat
    • Chlorine and regular water purification prevent infestation
    • Algae can be combated with chlorine, algaecides, hydrogen peroxide or hydrochloric acid

    Different types of algae in the pool

    Algae are plants that can be unicellular or multicellular. They need sunlight to grow, which is why algae only grow in exposed areas. The organisms are very undemanding and use CO2 and the sun as energy suppliers to produce carbohydrates and oxygen. There are particularly stubborn algae.

    scientific Happen Hints
    Red Algae Rhodophyta littoral zone of the sea Bacterial film in pools is incorrectly referred to as red algae
    Brown Algae Phaeophyta almost exclusively marine resistant organisms with filamentous structure
    Green Algae Chlorophyta over 50% of the species live in fresh water form floating particles or long threads
    Yellow Algae Xanthophyceae Freshwater often referred to as mustard algae
    Black Algae cyanobacteria mostly in fresh water no algae; take root in plaster and concrete

    Supposed white, red and black algae

    If shimmering red or black spots form on the pool walls, algae are usually not to blame. These are bacterial lawns that are caused by environmental influences and a lack of disinfection. Occasionally, these bacterial accumulations can also be white in color. The patches detach from the adhesive base and then float in the water. Sometimes deposits that come from the outside and settle to the bottom are mistaken for algae.

    cause of algae growth

    If the pH value is too high, algae growth is encouraged

    The pH value and the color of the water provide information about the water quality and show which cleaning measures are necessary. Ideally, the pH is around 7.4. Algae feel comfortable at higher values. Algae and bacteria are not always responsible for discolored water or deposits on the walls:

    • yellow-green water: Indication of increased iron concentration
    • milky water: Pollution by organic residues
    • slippery walls: algae growth or bacterial lawn
    • rough pool walls: calcification of the water

    How does algae form in the pool?

    If there is not enough anti-algae in the pool water, the risk of algae growth increases. The pH value also has an influence on algae growth. The organisms need nutrients to grow, which they get from leaves, hair, cosmetics or dander.

    Are algae dangerous?

    Algae in pools do not pose a health risk. Despite the unsightly color of the water, you can swim in the water without hesitation. However, the algae growth should not get out of hand, because some species then produce substances that are toxic to humans. This is especially true for cyanobacteria. They produce secondary metabolites that they do not necessarily need for their actual growth.

    digression

    algae bloom

    Elevated temperatures in combination with over-fertilization of the water body with phosphate can lead to so-called algae or water blooms. This describes a sudden and massive increase in algae and cyanobacteria. Depending on the species, the water surface turns green, red or blue. The water becomes very cloudy and only little light reaches the lower layers. Some algae and cyanobacteria produce toxic substances that can be dangerous for bathers. However, there are only about 50 species of algae that develop such toxins.

    When does algae form in the pool?

    Algae grow where there is little water circulation. Heat and changeable weather as well as residues in the water favor the development of algae. Therefore, algae growth mainly occurs in spring and summer. The most common types of algae in pools are green algae. Brown algae show up as deposits on the pool floor and walls. Yellow algae appear less frequently and develop a powdery precipitate on the bottom. Bacteria develop on the walls or on the floor as a result of a lack of cleaning routine.

    Remove and fight

    Fighting algae successfully usually requires chemical agents. This pollutes the water and there are health risks if the dosage is incorrect. To prevent this from happening in the first place, you should prevent algae growth with the right water treatment.

    Basics for proper cleaning:

    • remove coarse dirt with a net
    • Vacuum walls and floor
    • mechanical water treatment with pumps and filter systems
    • chemical water treatment
    • Water exchange by submersible pump

    Algae in the pool is not dangerous. However, they indicate an imbalance.

    chlorine

    Chlorine protects against algae, but should only be used in moderation

    Chlorine is the classic disinfectant in swimming pools. It prevents algae and bacteria from multiplying and kills them. Chlorine can also be used with existing algae growth. The concentration should be around three parts per million. If you have algae in the pool despite chlorine, various factors can come into question:

    • insufficient water flow
    • Foils act as flow brakes
    • chlorine concentration too low

    algaecide

    These biocides are effective against the formation of algae. If used regularly, it can have a preventive effect. If the pool is already infested with algae, these agents usually no longer help. The organisms multiply despite the algaecide. Many algaecides have high levels of metals, which can lead to further problems. If you still want to use these biocides, the agents should be free of copper.

    copper sulfate

    Copper is an effective agent that stops the growth of most algae. Copper sulphate used to be the main ingredient in algaecides. Today it is only used occasionally. It also kills the extremely resistant black algae on the walls. However, it also has disadvantages. Pool water that has been treated with copper sulphate must not be discharged into the sewage system. It must be disposed of properly as the heavy metal is harmful to aquatic organisms.

    • Bacteria and viruses are not killed
    • Algae can develop resistance
    • increased copper content for too black spots or yellowish discolorations

    hydrogen peroxide

    An alternative to chlorine is water treatment with active oxygen. If hydrogen peroxide is added to the pool water, UV radiation causes the formation of hydroxyl radicals. These have a much stronger effect than the peroxide and ensure the breakdown of organic impurities. The disadvantages are that the water can quickly become unbalanced. This is especially the case in the high season. If chlorine and hydrogen peroxide are used at the same time, the water can become cloudy and a water change is necessary.

    hydrochloric acid

    Acids are used to lower the pH value and curb algae growth. Hydrochloric acid is a highly corrosive liquid that should not be used in private pools. Another disadvantage is that chlorides get into the water with the hydrochloric acid. These can promote corrosion.

    Inappropriate means

    There are some home remedies that should not be put in the pool. Either they are not effective or they do not solve the algae problem. Therefore, consider your methods well in advance and weigh the possible dangers against the benefits.

    vitamin C

    Ascorbic acid ensures in the short term that the water clouded by algae appears clear again. This phenomenon is based on a chemical reaction that makes iron particles invisible. However, vitamin C is not able to remove these particles or fight the algae. The basic problem is still there, which is why this home remedy is not suitable for combating algae.

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    soda

    Washing soda or sodium carbonate can be added to pool water to raise the pH if it is too low. It takes about five grams of soda per 1.00 liters of water to raise the pH value by 0.2 points. However, this measure cannot combat the growth of algae, since algae prefer to live in water with a pH value of over 7.5. Soda should not be confused with baking soda, because behind it is sodium bicarbonate.

    Home remedies for algae in the pool

    Cleaning the pool without chemicals is good for your health. Since water is sensitive to the addition of various agents, the correct dosage is extremely important. The most effective weapon in combating algae is fresh water. A complete water exchange makes sense if there is heavy algae growth.

    salt

    Many pool owners use table salt to destroy algae. Slightly salty water not only has an antiseptic effect, but can also kill freshwater algae. Therefore, salt systems are used that work with a salt concentration of 0.4 to 0.7 percent. Salt can also be used to combat algae. However, over time, the salt will attack metallic objects and in the worst case, all the water will have to be replaced.

    vinegar

    Just like citric acid, vinegar is a natural agent that can lower the pH value. With the consumption of oxygen, acetic acid breaks down and salts remain. This can kill living creatures in the water if sufficient water circulation is provided. The downside is that vinegar can encourage bacterial growth.

    tips

    You can buy test strips at the pharmacy that you can use to test the pH value.

    water treatment

    Pool water should be cleaned regularly

    To prevent algae growth in the first place, the water must be cleaned and treated regularly. After the winter season, the pool should be cleaned thoroughly so that no residues affect the water. Adding fresh water to the pool regularly is just as important. The older the water, the higher the risk of algae formation. Since the organisms need light to grow, an opaque tarpaulin is necessary as a cover. Remove corroded items and dead organic material

    • pH should be between 7.0 and 7.4
    • Chlorine value is ideally 0.3 to 0.2 milligrams per liter
    • Check values weekly

    tips

    Before going on vacation, you should perform a chlorine shock to destroy organic compounds and bacteria.

    sand filter

    A correctly dimensioned sand filter system cleans the entire pool water with the help of sand with a grain size of 0.5 to 0.8 millimeters. If the water is pumped through the filter system, small suspended particles remain and the water enters the pool clean.

    So that the filter performance is not impaired, the dirt in the drain must be backwashed. Here, the dirt particles are flushed out of the filter into the waste water. This process should be repeated every week to prevent particles from accumulating in the water. The quartz sand (€15.85) should be replaced every two years.

    cartridge filter

    These filter systems are an alternative to the sand filter, which are equipped with a paper cartridge. Here, too, dirt particles are removed by pumping the pool water through the filter. In order to remove the filtered particles, the cartridge must be hosed down or replaced. Leaves, small stones or sand are not filtered out and must be removed with a pool vacuum.

    frequently asked Questions

    What causes algae in the pool?

    Algae need nutrients, warmth and an increased pH value

    Algae are plant organisms that need nutrients, warm temperatures, and sunlight to grow. They are comfortable at higher pH levels, above 7.5. When the concentration of disinfectants in the water decreases and the environmental conditions are optimal, algae can form overnight in spring and summer.

    Algae in the pool and still swim?

    Most algae that settle in the pool are not harmful, toxic or dangerous. Only a few species of algae develop toxic substances during the algal bloom, when they multiply en masse. The bacteria, which are often mistaken for red or black algae, are also harmless. You can easily bathe in the water. The only danger is the cloudiness of the water, which causes green floating algae. They obstruct visibility when diving.

    What helps against algae in the pool?

    The floating threads should first be removed with the landing net. Algae and bacterial growth must be mechanically removed from the walls and floor, as these can sometimes develop stubborn roots. Measure the water parameters to determine if they are within the normal range. Shock chlorination proves effective in combating algae. If the growth is strong, a water change is recommended. Also remember to clean all filter systems.

    What to do against algae and worms in the pool?

    When ambient temperatures rise, algae and small red worms can suddenly grow. Behind the worms are the larvae of the mosquitoes, which prefer to lay their eggs on the water. These creatures cannot survive if the water is properly disinfected. Chlorination can help. In addition, the filter systems should be checked and cleaned if necessary.

    Why do I have dead algae in the pool every day?

    Flocculants are added to the skimmer because they bind the finest dirt particles. It is added to the skimmer which should be run until completely dissolved. If it is switched off, the agent can flake in the water. As a result, structures can form in the water that are reminiscent of white algae. If green algae appear regularly, you should consider a short-term chlorine shock.

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Garden design